Work on the molecular characterization of Na ion and K ion transport, utilizing our purified shark rectal gland or electroplax (sodium plus potassium)-activated adenosine triphosphatase (Na,K-ATPase) will be continued. The isolation of a chemically homogeneous active site peptide and the sequencing of amino acids in this peptide will be continued, utilizing tagging of the active site with tritium by converting the aspartyl-beta-phosphate residue to (3H) homoserine by reduction with (3H) sodium borohydride. We will continue our studies of the biosynthesis of the Na,K-ATPase in electroplax tissue and in the brine shrimp. Phospholipids other than egg lecithin in forming Na,K-ATPase vesicles and in reconstituting the coupled transports of Na ion and K ion will be investigated. Lecithins with known fatty acid compositions will be investigated, and Arrhenius plots of reconstituted Na ion and K ion transport will be attempted to see if breaks occur at the "melting points" of known phospholipids. Further attempts will be made to form vesicles and reconstitute Na ion and K ion from the purified electroplax Na,K-ATPase. The purification procedure presently used involves a zonal centrifugation step which is complicated, time consuming, and expensive. Attempts will be made to substitute ion exchange chromatography for the zonal step with the aim of obtaining comparable yields and comparable specific activity as is now obtained with purification method involving the zonal step. BIBLIOGRAPHIC REFERENCES: Hokin, L.E. Purification and molecular properties of the (sodium plus potassium)-adenosinetriphosphatase and reconstitution of coupled sodium and potassium transport in phospholipid vesicles containing purified enzyme. J. Exp. Zool. 194, 197 (1975). Hilden, S. and Hokin, L.E. Coupled Na ion -K ion transport in vesicles containing a purified (NaK)-ATPase and only phosphatidyl choline. Biochem. Biophys. Res. Commun. 69, 52l (1976).